package cn.lcsjsxy.yxc.ioandnetwork;

import org.junit.jupiter.api.Test;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

/**
 * RandomAccessFile的使用
 * 1.RandomAccessFile直接继承于java.long.Object类，实现了DataInput和DataOutput接口
 * 2.RandomAccessFile既可以作为一个输入流，又可以作为一个输出流
 * 3.如果RandomAccessFile作为输出流时，写出到的文件如果不存在，则在执行过程中自动创建
 *   如果写出到的文件存在，则会对原有文件内容进行覆盖，（默认情况下，从头覆盖）
 * 4.可以通过相关的操做，实现RandomAccessFile"插入"数据的效果
 */
public class RandomAccessFileTest {

    @Test
    public void test1(){
        RandomAccessFile raf1= null;
        RandomAccessFile raf2= null;
        try {
            raf1 = new RandomAccessFile(new File("helloCopy.txt"),"r");
            raf2 = new RandomAccessFile(new File("random.txt"),"rw");

            byte[] buffer=new byte[1024];
            int len;
            while ((len=raf1.read(buffer))!=-1){
                raf2.write(buffer,0,len);
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            try {
                if (raf1!=null)
                    raf1.close();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }

            try {
                if (raf2!=null)
                    raf2.close();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

    @Test
    public void test2(){
        RandomAccessFile raf1=null;
        try {
            raf1=new RandomAccessFile("hello.txt","rw");
            raf1.seek(3);  //将指针调到角标为3的位置
            raf1.write("xyz".getBytes());
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            try {
                if (raf1!=null){
                    raf1.close();
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

    /*
     使用RandomAccessFile实现数据的插入效果
    */
    @Test
    public void test3(){
        RandomAccessFile raf1=null;
        try {
            raf1=new RandomAccessFile("hello.txt","rw");

            //保存指针3后面的所有数据到StringBuilder中
            byte[] buffer=new byte[20];
            StringBuilder builder=new StringBuilder((int) new File("hello.txt").length());
            int len;
            while((len=raf1.read(buffer))!=-1){
                builder.append(new String(buffer,0,len));
            }

            //调回指针.写入"xyz"
            raf1.seek(3);
            raf1.write("xyz".getBytes());

            //将StringBuilder中的数据写入到文件中
            raf1.write(builder.toString().getBytes());

        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            try {
                if (raf1!=null){
                    raf1.close();
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }
}
